1. Field of the Invention
The present invention relates to an optical member, and more particularly to an optical member used in an optical instrument such as a projector which composes images formed by three liquid crystal panels, and enlarges and projects a composed image onto a screen.
2. Description of the Related Art
FIG. 1 schematically illustrates a main part of a conventional three-panel type projector.
Referring to FIG. 1, the projector is chiefly composed of a projection lens 101 and an illumination box 102. The illumination box 102 has a light source 103, dichroic mirrors 104 and 105 for color separation, dichroic mirrors 106 and 107 for color composition, reflecting mirrors 108 and 109, and liquid crystal panels 110, 111 and 112.
In the projector shown in FIG. 1, white light emitted from the light source 103 is separated into three colors, red, green, and blue, by the dichroic mirrors 104 and 105, and each color light illuminates liquid crystal panels 110, 111 and 112, respectively. Images of the three colors of red, green, and blue, respectively formed on the liquid crystal panels are composed by the dichroic mirrors 106 and 107, and the composed image is enlarged and projected onto a screen (not shown) by the projection lens 101.
In the above conventional projector, however, components are individually provided in the illumination box 102. Thus, because there may be some inaccuracy in mounting each component, each of the red, green, and blue color images may be displaced. That is, the mounting inaccuracies may cause errors movement and rotation of a focus. To correct for these inaccuracies, each image on the screen can be matched by fine adjustment of the positions of the liquid crystal panels 110 to 112. However, since the displacements of the images vary with a combination of mounting errors of the separate optical components, the adjustment becomes complicated and makes manufacturing the apparatus more difficult.
In addition, other factors, such as impact on the illumination box 102 and temperature changes cause a partial position error of each component, so that the adjusted images are disturbed again.